Dehydrogenation catalyst



United States Patent 3,448,058 DEHYDROGENATION CATALYST Melvin R.Arnold, Louisville, Ky., assignor to Chemetron Corporation, Chicago,11]., a corporation of Delaware No Drawing. Filed Nov. 12, 1965, Ser.No. 507,553 Int. Cl. B01 11/82 US. Cl. 252-443 6 Claims This inventionrelates to dehydrogenation catalysts and an improved method for theirproduction. More particularly, it relates to the production of catalystssuitable for the dehydrogenation of alkyl aromatic hydrocarbons toalkenyl aromatic hydrocarbons and to the catalysts so produced.

It is well known that styrene is produced commercially by the catalyticdehydrogenation of ethylbenzene. The process is usually carried out bypassing ethylbenzene and a relatively large proportion of steam, forexample, 2-30 moles of steam per mole of hydrocarbon, over a bed of asuitable catalyst at elevated temperatures. The catalysts used in theprocess usually contain as a primary active constituent certain metalsof Groups 1V to VIII of the Periodic Table either in their free form or,preferably, in the form of various of their compounds such as theoxides, sulfides, phosphates, etc. Generally, mixtures of two, three ormore of such compounds are employed. Some of these catalysts, however,are characterized by certain disadvantages such as low conversion and/orselectivity of reaction, poor physical strength, short catalyst life,and necessity for frequent regeneration. Typical catalysts which havebeen found to have a minimum of these disadvantages are alkalized ironoxide catalysts wherein an alkali metal or alkaline earth metal compoundis employed as a promoter, said promoter being usually a compound ofpotassium. These catalysts are autoregenerative under conditions atwhich the dehydrogenation reaction is effected, that is, they arecapable of being continually regenerated under the conditions of thereaction. This feature obviates the necessity for interrupting theprocess and regenerating the catalyst, a procedure which includesburning the carbon deposits off the surface of the catalyst particles,as is required with other dehydrogenation catalysts.

In the copending application of Emerson H. Lee, Ser. No. 507,514, filedof even date herewith now US. Patent 3,387,053 issued on June 4, 1968,there are described and claimed a group of dehydrogenation catalystswhich comprise iron oxide as the active catalytic agent, about 1% toabout 8% by weight of zinc oxide and/or copper oxide intimatelydispersed in the matrix of iron oxide, and an alkali promoter such aspotassium carbonate. In these catalysts the ingredients are intimatelydispersed so that the magnetic susceptibility of the catalystcomposition prior to use is in the range from about 30 l0- to about300x10 centimeter-gram-second units (c.g.s.u.) and the surface area ofthe catalyst composition prior to use is in the range from about 1 toabout 5 square meters per gram. These catalysts are produced bycoprecipitation of iron oxide and zinc oxide and/or copper oxide from asolution containing ferrous, zinc and/or copper ions by the addition ofalkali. The mixed precipitate of iron, zinc and/or copper oxides is airblown at elevated temperature at a pH in the range from 6.8 to 7.2,Washed free of soluble materials, filtered and dried. The mixture ofiron, zinc and/or copper oxides so produced is mulled with an alkalipromoter and a binding agent such as portland cement, and formed intocatalyst shapes.

In accordance with my invention, intimately dispersed compositions ofiron oxide and zinc oxide and/or copper oxide are produced by wetmulling the metal oxides with aqueous ammonia. In this manner adispersion of the metal oxides is produced which has a high magneticsusceptibility in the range of about 30x10" to about 300x lO c.g.s.u.This procedure is simpler and less expensive than the coprecipitationprocedure described above and produces metal oxide catalyst compositionsof high activity in dehydrogenation reactions.

It is an object of this invention to provide an improved method ofproducing dehydrogenation catalyst compositions. It is a further objectto provide dehydrogenation catalysts produced by the improved method.Another object is to provide a method for producing intimately dispersedmetal oxide catalyst compositions by a wet mulling technique. A furtherobject is to provide improved catalysts for the dehydrogenation of alkylaromatic hydrocarbons to alkenyl aromatic hydrocarbons and an improvedmethod for their production. These and other objects are apparent fromand are achieved in accordance with the following disclosure.

As described in the copending application of Emerson H. Lee referred toabove, an improved dehydrogenation catalyst comprises iron oxide as theactive catalytic agent, from about 1% to about 8% by Weight of a matrixpromoter, i.e., an oxide of a metal selected from the group consistingof zinc and copper, intimately dispersed in the matrix of said ironoxide, the degree of said dispersion being such as to characterize thecatalyst prior to use by a magnetic susceptibility in the range fromabout 30 to about 300 l0- centimeter-gram-second unit (c.g.s.u.), and analkali promoter, said catalyst composition having a surface area in therange from about 1 to about 5 square meters per gram (m. /g.). In thepreferred embodiment of the invention, the metal oxide intimatelydispersed in the matrix of the iron oxide is zinc oxide and the alkalipromoter is a compound of an alkali metal, preferably potassium. Othercompounds may be present in addition to the three essential ingredientssuch as stabilizers, diluents, binders, and the like.

The matrix promoter is zinc or copper oxide or a mixture thereof, but iscan be produced from salts of those metals, in addition to oxides orhydroxides thereof. For instance, zinc acetate, zinc carbonate, zincchloride, zinc nitrate, copper acetate, copper chloride, copper nitrateand copper carbonate can be used as the source of zinc and copperoxides. These salts readily form metal-ammine complexes with ammoniawhich aid in the formation of metal ferrites.

The matrix promoter is believed to function as a modifier or conditionerof the iron oxide component of the catalyst rather than to serve as astabilizer to prevent the promoter from volatilizing or the catalystfrom becoming inactive as is taught in the art. Accordingly, in thehighly selective catalyst compositions of the present invention, acritical concentration of the second metal oxide, i.e., the matrixpromoter, is intimately incorporated into the iron oxide matrix makingthe resulting composition distinguishable on the basis of its magneticsusceptibility. This magnetic susceptibility reflects the existence ofthe ferrites of zinc and/or copper, which are magnetic, in the catalystcomposition.

By the procedure of my invention, a mixture of iron oxide and zincand/or copper oxide is mulled with an aqueous ammonia solutioncontaining an excess of ammonia over that required to convert the metalsto metal ammine ions, such as Zn(NH Zn(NH Cu(NH and Zn(NH Themetal-ammine complexes aid in the formation of zinc and copper ferriteswhich contribute to the magnetic susceptibility of the compositions. Itis desirable that the amount of water during mulling be sufficient toform a paste or slurry which is readily mulled. Concentrated aquaammonia (28% NH OH solution) is preferred but other concentrations aresuitable. The wet mulling operation is continued until a dried specimenexhibits magnetic susceptibility in the range from about 30 10- to about300 10 c.g.s.u. This is usually achieved in hour to 1 hour, depending onthe size of the batch. Then the alkali promoter and other components areadded and the resulting mixture is mulled to a paste, preferably ofsuitable consistency for extrusion to catalyst shapes. The mixture afterbeing formed into catalyst shapes is air cured and calcined.

The catalyst produced by my invention contains iron oxide as thepredominating active dehydrogenating constituent. A convenient andeconomical source of iron oxide is in the form of commercial pigmentswhich are of uniform purity and particle size. However, iron oxides mayalso be prepared by the thermal decomposition of iron compounds such asferric nitrate, ferric oxalate, and the like or by precipitation fromsolutions of iron salts such as ferric nitrate, ferrous sulfate, etc.,followed by thermal decomposition. Generally, however, the latterprocedures do not produce an oxide of uniform characteristics and highpurity at a cost competitive with that of commercial pigments. Theconcentration of the iron oxide in the finished catalyst may vary over awide range. The catalyst should contain on a finished basis at leastabout 35 by weight of iron oxide. Preferably, the concentration of ironoxide is maintained in the range from about 45% to about 95% by weight.

The concentration of the metal oxide employed as the matrix promoteradded to the iron oxide is critical. Amounts employed are those in therange from about 1% to about 8% by weight of the total catalystcomposition. Preferably, the matrix promoter should be present in theamounts from about 2% to about by weight of the total catalystcomposition.

An alkali promoter is also an essential constituent of the catalyst.Compounds of the alkali metals such as the oxides or compoundsconvertible at least in part under dehydrogenation conditions to theoxides such as the hydroxides, the carbonates, the bicarbonates, thephosphates, the borates, the acetates, the chromates and dichromates,and the like are useful as promoters. Of the alkali metal compounds,potassium compounds are preferred. Cesium and rubidium compounds aresuitable but are generally not used because of their high cost. Whilethe sodium compounds are less expensive than those of potassium, thelatter are considered to be superior as promoters. A particularlypreferred promoter is potassium carbonate. The amount of promoter in thecatalyst may vary from about 0.5% by weight of the catalyst up to about50% by weight or more. Preferably, the alkali metal promoter isincorporated in the catalyst in amounts from about 5% to about 35% byweight. If it is desired to control the dehydrogenation of ethylbenzeneso that the least possible amount of toluene will be produced while themaximum yield of styrene is being attained, a composite promoter can beused. Such a promoter is one containing a potassium compound and acompound of a metal chosen from the group consisting of sodium, lithium,barium, magnesium, and calcium wherein the potassium compoundconstitutes at least 1% by weight of the total catalyst composition andthe weight ratio of the second metal compound to the potassium compoundis maintained within the range from about 1:1 to about 5:1 andpreferably from about 1:1 to about 2:1 as described in the Emerson H.Lee Patent 3,100,234.

As indicated above, other ingredients may be present, as desired, in thecatalyst composition. Heavy metal oxides more difircultly reducible thaniron oxide which function as stabilizers can be included, for example.The concentration of such stabilizers is not critical. Only smallamounts are required. Chromium oxide is the preferred stabilizer andthis compound is generally employed in amounts from about 1% to about 5%by weight. Diluent materials such as alumina, zirconia, beryllia, andasbestos can also be incorporated in the catalyst as can binding agents,for example, silicates, hydraulic cements such as Portland cement,calcium aluminate cement, kaolin, ball 4 clay and the like, if desired,which impart structural stability to the catalyst composition.

The shape and size of the catalyst particles are not critical. Forexample, the catalyst may be in the form of pellets, powders, pills,tablets, spheres, saddles, etc. Symmetrical pills of inch to inch indiameter and A inch to 1 inch in length are considered to besatisfactory. The preferred size of the catalyst particles for mostcommercial operations is usually from to inch in diameter.

Surface area of the catalyst, however, is a critical factor. Even if thematrix promoter is present as determined by magnetic susceptibilitymeasurements in the range specified, the desired selectivity of reactionis not obtained if the surface area of available surface of the catalystis too large. Thus, the improved catalysts of the invention are thosewith a surface area or available surface from about 1 to about 5 squaremeters per gram. It is preferred to adjust the surface area during themanufacture of the catalyst; however, with some formulations, catalystscan be prepared with higher surface areas allowing for subsequentsurface area reduction to the preferred range during use of thecatalyst.

My invention is disclosed in further detail by means of the followingexample. It will be understood by those skilled in the art that variousmodifications of these procedures can be made without departing from theinvention. For instance, the quantities of materials can be variedwithin the ranges set forth herein, the times of various operations canbe varied with respect to the size of the batches and the type ofequipment used, and temperatures and concentrations can be adjusted foroptimum efiiciency within the ranges set forth.

EXAMPLE 1 A pair of catalysts was prepared by the wet mulling procedurewith definite amounts of iron oxide and zinc oxide or definite amountsof iron oxide and copper oxide. The catalysts as prepared both containedabout 26% potassium carbonate (K CO as a promoter, 2.5% chromic oxide(Cr O as a stabilizer, about 20% portland cement as a binder, and afixed amount of iron oxide as the active catalytic agent with eitherzinc oxide or copper oxide as a matrix promoter.

An iron oxide-zinc oxide catalyst composition was produced by thefollowing procedure:

There was placed in a Simpson Mix Muller 2772 parts by weight of pigmentgrade iron oxide (Fe O and 300 parts by weight of zinc oxide (ZnO). Thecomponents were mixed dry for five minutes. Next there was added 1500parts by weight of a 28% 'NH OH solution as the mulling was continuedfor five minutes while the solution was added. The thus wetted mix wasthen mulled for 15 minutes, and at the end of this time 1578 parts byweight of postassium carbonate (K CO was added, followed by 150 parts byweight of chromium oxide (Cr O After the promoter and stabilizer hadthus been added, there was mixed in 1200 parts by weight of portlandcement and parts by weight of water. After ten minutes additionalmixing, the mass was extruded as inch diameter extrusions.

The extrusions were cured in air for six days and then calcined for twohours at 250 F., two hours at 400 F. and six hours at 1300 F.

The analysis of this catalyst (No. 1) was as follows:

A second catalyst (No. 2) was produced by the same procedure but with300 parts by weight of copper oxide (CuO) in lieu of the Zinc oxide.

The specific surface area or available surface of both of thesecatalysts was determined and the magnetic susceptibility of each of themwas measured.

Experiments were conducted to determine the elfectiveness of thesecatalysts for the production of styrene.

the life of such a catalyst is significantly increased over that ofconventional iron oxide catalysts.

While the invention has been illustrated specifically by thedehydrogenation of ethylbenzene to styrene, the catalysts of theinvention are equally useful in the dehydro- Simnltaneously, acommercially available alkali-progenation of various other alkylaromatic hydrocarbons moted iron oxide catalyst was tested. Allcatalysts were having an alkyl side chain of at least two carbon atomsemployed in the form of inch extrusions. The dehy- Such as, for example,propylbenzene, diethylbenzene, ethyldrogenation of ethylbenzene usingthese catalysts was efol ene, propyltoluene, ethylnaphthalene,diethylnaphfected in an isothermally operated integral reactor thalene,diethyldiphehyl and the like to the corresponding consisting of a 5 ft.stainless steel tube 1% in. inside l y aromatic hydrocarbons. Likewise,the catalysis of diameter heated b electrical means and engaged in anthe invention are suitable fOI USE in the PIOdUCilOIl Of insulatedjacket. The reactor was packed with catalyst by diolefihs ydehydrogenation of mohoolefihs having at Pouring h i 1 i h b h h a f l tleast four non-quaternary carbon atoms inastraight chain. obtain aloosely packed bed about 43 in. deep supported y are Particularlyuseful, p in the P on a stainless steel screen. Sample taps and mermtion of butadiene from butylene and are also applicable couples reachinginto the catalyst bed were provided at and advantageous for theProduction of other diolefihs 6-in. intervals along the length of thebed. The temperaand Particularly conjugated diolefifls Such as P p yture of the catalyst bed was brought up to about 300 C. isoprehe, hVarious hexadiehes and the like from the with nitrogen flowing throughthe reactor. Steam was 2 eonespohdlhg mohoolefihss then introduced andthe temperature was raised to 600 I clalm: C. and allowed to remain atthis level overnight for pre- In en'lethod of p cmg a dehydrogenationcataconditioning of the catalyst. Steam and ethylbenzene lyst cohtammgleast 35% by Welght of oxlde as (99.7%) in a weight ratio of about 2.2:1was then fed the i catalytlc f from 1% to about to the reactor at a gashourly space velocity of 595 (volby Welght of a matrlX PIOIIIOteI OfZlnc or copper oxides ume of feed gases at standard temperature andpressure and from about to about 5O% by welglft of a1 ka11 per volume ofcatalyst per hour) while it was maintained PIQmOteI step Yvhlch COmPnSFSmulhng 531d at a temperature of about 600 C. Conversions over a oxlfieand sald mamx profhoter Wlth aqueou? ammom? Wide range were measured bymeans of Samples drawn untll the resulting composltlon has a magneticsuscept1- from the taps in the reactor; flows from the sample taps 3Oblhty tha range from about X10 6 to about never exceeded about 10% ofthe total flow to avoid 300 1O 6 changing the flow pattern in thereactor. The efiluent gas Methpd of claim 1 Wherem the amount of matrixstreams passed from the reactor into a water-cooled conprqmoter 18 fromabout 2% to about 5 of the catalyst denser and the condensates werecollected in receiving welght' flasks. Non-condensible gas was passedthrough a wet test Method of clalm 2 Wherem an alkah promoter eqmvmeterand vented after measuring. Samples of the organic alept 9 about 5% to.about 35% the dry catalyst condensates were analyzed for styrene,benzene, and tolgggifi g subsequently Incorporated the catalyst uenewith precautions being taken to prevent any loss of benzene and toluenefrom the sample. Selectivity for sty- Method of clalm 3 wherem the alkahpromoter is rene for each catalyst tested is recorded in Table I belowpotassium carbonat? together with the composition, the specific surfacearea, i z of i 4 g fi oxlde eqmyalerit and the magnetic susceptibilityof the catalysts. Selectivity to a out o a out 5 o 6 dry catalystvii-eight Is is defined as follows: subsequently lncorporated 1n thecatalyst composltion.

M 1 st en 6. Msithod of clalm 5 wherein the matrlx promoter 1s oes yr ezincoxie. Moles (Styrene-l-Benzene-l-Toluene) X100 All selectivity dataare for the catalytic reaction only, corrections based on experimentaldetermination having been made for any thermal reaction occurring.

TABLE Amt. of Magnetic Net conv. Selectivity matrix Surfacesusceptiacross catato styrene F8203 Matrix promoter area bility (vol.)yst bed mole Catalyst N o. (wtpercent) promoter (wt. percent) (mfl/g.)(cgsuXm- 1 percent Hours 1 46.2 ZnO 5.0 2.3 195.8 45.9 94.6

54.7 93.6} 1,097 60.5 91.8 2 46.2 CuO 5.0 3.2 202.5 45.7 94. s}

53.6 93.6 944 61.1 92.8 Commercial catalyst None 4. 5 16.8 45. 9 93. 8

56.1 91.8 1 Wt. percent styrene in dehydrogeuated mixture.

References Cited UNITED STATES PATENTS The selectivity data presented inTable 1 demonstrate 3-209049 9/1965 Pitzel 260 680 clearly thesuperiority of the catalysts produced by this 3,084,125 4/1963Sonderquist 252430 invention over the iron oxide catalysts in the art.When the catalyst has a magnetic susceptibility from about 30 PATRICKGARVIN Primary Exammer' to about 300x 10" c.g.s.u. it is much moreselective for U5. CL

styrene production than are catalysts with lower magneticsusceptibility. As a consequence styrene production over

2. METHOD OF CLAIM 1 WHEREIN THE AMOUNT OF MATRIX PROMOTER IS FROM ABOUT2% TO ABOUT 5% OF THE CATALYST WEIGHT.
 3. METHOD OF CLAIM 2 WHEREIN ANALKALI PROMOTER EQUIVALENT TO ABOUT 5% TO ABOUT 35% OF THE DRY CATALYSTWEIGHT IS SUBSEQUENTLY INCORPORTED IN THE CATALYST COMPOSITION. 4.METHOD OF CLAIM 3 WHEREIN THE ALKALI PROMOTER IS POTASSIUM CARBONATE.